Sensory Receptors 13.3

Question 1

How does the body detect changes in the environment?

Answer 1

There are sensory receptors which are groups of specialised cells on sense organs like skin, eye, ear etc…

Question 2

How do sensory receptors work?

Answer 2

They detect a stimuli and convert this into a nervous impulse that is then transmitted to the CNS, normally the brain, which will then coordinate a response and send the impulse to the effector cells that will produce a response.

Question 3

What are the features of a sensory receptor?

Answer 3

• They are specific to a single type of stimuli

- They act as a transducer by converting the stimuli into a nervous impulse.

Question 4

Types of receptors in animals

Answer 4

Mechanoreceptor, Chemoreceptor, Thermoreceptor, Photoreceptor

Question 5

Mechanoreceptor

Answer 5

Responds to pressure and movement, an example is the Pacinian Corpuscle and is located on the skin

Question 6

Chemoreceptor

Answer 6

Responds to chemicals, an example is an olfactory receptor and is located in the nose to detect smell

Question 7

Thermoreceptor

Answer 7

Responds to changes in temperature mainly heat, an example is end bulbs of Krause which are on the tongue

Question 8

Photoreceptor

Answer 8

Responds to light, an example is cone cells in the eye.

Question 9

What is produced when a stimuli is detected?

Answer 9

The receptors will detect the stimuli and act as transducers by making a generator potential which acts as the nervous impulse.

Question 10

Pacinian Corpuscle

Answer 10

This is a mechanoreceptor that detects changes in pressure and movement. It is found in a deep layer of the skin and a re most abundant in the soles of feet and fingertips as well as joints

Question 11

Structure of Pacinian Corpuscle

Answer 11

The end of the sensory neurones is located in the centre of the corpuscle and is surrounded by layers of connective tissue. Between these layers, there is viscous gel that separates them and helps transmit more movement. It also has a blood capillary on the outside and a capsule which holds it all together. The neurone in the structure is responsible for transporting sodium ions across the membrane and therefore have sodium ion channels. The end of the neurone has a special channel called a stretch mediated sodium channel which allows it to change shape and when they stretch, they can increase the permeability to sodium

Question 12

How is pressure converted into a nervous impulse?

Answer 12

• In its normal state, the stretch mediated sodium ion channels in the sensory neurone are too narrow to allow sodium ions to pass through. This means the neurone of the Pacinian Corpuscle is at resting potential. The membrane is polarised as there are more positive ions on the outside than inside of the cell.
• When pressure is applied, the corpuscle will change shape and the membrane surround the neurone will stretch.
• When the membrane stretches, the sodium ion channels present will open which mean sodium ions will diffuse down the electrochemical gradient, into the neurone
• All the positive sodium ions entering the neurone will change the potential of the neurones membrane so it will become depolarised. This results in a generator potential
• This generator potential will create an action potential ( nerve impulse) which is then transmitted across the sensory neurone and also the CNS